1. Field of the Invention
The present invention relates to a communication control device for data between a computer and peripheral devices thereof, and more specifically to a communication control device capable of preventing loss of communication data using a USB line.
2. Description of the Related Art
FIG. 5 is a conceptual view illustrating a conventional data communication method, and shows communication control between a host computer (hereinafter, referred to as “host”) 1 and a peripheral device 2.
The host 1 and the peripheral device 2 are connected through a universal serial bus (“USB”) line 3, and data communication therebetween using digital signals can be performed.
Storage means 2a is provided in the peripheral device 2, and the data generated by the peripheral device 2 is stored in the storage means 2a. 
When the data generated by the peripheral device 2 is stored in the storage means 2a, the peripheral device 2 transmits the data from the storage means 2a to the host 1 in response to a data transmission request signal (“IN command”) from the host 1. On the other hand, when the data is not stored in the storage means 2a, the peripheral device 2 sends a negative acknowledge (“NAK”) signal indicative of absence of data to the host 1.
In this manner, the host 1 transmits the data transmission request signal to the peripheral device 2 for every predetermined period of time, and the peripheral device 2 transmits the NAK signal or the data to the host in response to the data transmission request signal, so that interactive data communication between the host 1 and the peripheral device 2 is performed.
(Patent Document 1)
Japanese Unexamined Patent Application Publication No. 10-145435.
However, even when a software hierarchy of the host 1 for accepting the data is not prepared completely, a hardware hierarchy of the host 1 may output the data transmission request signal to the peripheral device 2. At that time, if the data is not stored in the storage means 2a of the peripheral device 2, the data is sent from the peripheral device 2 to the host 1, and as a result, a problem occurs in which the host 1 may lose the data.
In particular, right after the host 1 is powered on or when the host 1 is being restored from a sleep mode or a suspended mode, etc. by means of a resume function, the peripheral device 2 may send the data stored in the storage means 2a to the host 1. Then, since the data is transmitted from the peripheral device 2 to the host 1 before the software hierarchy reaches a normal operation mode, the aforementioned phenomenon can easily occur.
Such phenomenon is apt to take place in case, for example, wherein a hard disk in the host 1 is a digital video device for recording television broadcasting, etc. That is, when a person watches the television broadcasting in a state that the host 1 is in the sleep mode and the like, he/she may intend to record the broadcasting in the hard disk of the host 1. Then, even if a resume signal is transmitted from an input device (peripheral device) such as a keyboard or a remote control (not shown) to the host 1, it is usual that one minute or more is taken till the host 1 is restored and then the data communication between the input device and the host 1 is switched into the normal operation mode.
For this reason, when data required for video recording such as recording start data (REC data) or channel data of the television broadcasting is inputted to the input device, the storage means 2a in the input device stores the data. However, if the hardware hierarchy outputs the data transmission request signal to the input device before the software hierarchy of the host 1 starts, the data required for video recording may be lost. As a result, a problem may occur wherein the video recording does not start even after the host 1 is restored or a problem of other channel being recorded may occur.
With regard to such problems, even when the peripheral device 2 receives the data transmission request signal, a constitution wherein the NAK signal is continuously transmitted for a certain period of time until the software hierarchy completely starts after outputting resume signals, but data is not transmitted may be considered desirable.
However, since the time required for the host 1 in receipt of the resume signal to reach the normal operation mode depends upon environment such as the hardware constituting the host 1 or the operating system built in the host 1, it is difficult to determine a certain period of time during which the NAK signal is continuously transmitted. Thus, such constitution may not be considered proper/suitable.